Aqueous self-crosslinking copolymer dispersions, a process for preparing them and their use in binders for coating materials

ABSTRACT

Aqueous self-crosslinking copolymer dispersions ABC obtainable by free-radically initiated copolymerization in the first stage of a monomer mixture A comprising olefinically unsaturated monomers A1 having carbonyl groups, unsaturated carboxylic acids or monoesters of unsaturated dicarboxylic acids A2, monomers A3 selected from vinylaromatic compounds, n-butyl methacrylate and also alkyl esters of unsaturated carboxylic acids or dialkyl esters of unsaturated dicarboxylic acids, esters A4 selected from alkyl esters of unsaturated carboxylic acids of dialkyl esters of unsaturated dicarboxylic acids, and other free-radically polymerizable monomers A5, and subsequent addition of a second monomer mixture B and further polymerization in the second stage, the mixture B comprising olefinically unsaturated monomers B1 corresponding to A1, esters B2 corresponding to A4, and monomers B3 corresponding to A5, and subsequently adding compounds C having hydrazine or hydrazide groups.

RELATED APPLICATIONS

[0001] This application claims priority to Austrian application No.A1739/98, filed Oct. 19, 1998, herein incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to aqueous self-crosslinking copolymerdispersions having a core-shell structure, at least some of the monomersforming the copolymer in the core having carbonyl groups and carboxylgroups as well as free-radically polymerizable olefinically unsaturatedgroups, and comprising dicarboxylic dihydrazides or bishydrazinecompounds. The invention additionally relates to a two-stage process forpreparing these aqueous self-crosslinking copolymer dispersions and totheir use as binders for storage-stable one-component coating materialswhich crosslink at room temperature or at elevated temperature.

[0004] 2. Description of the Related Art

[0005] EP-A 0 649 865 discloses self-crosslinking carbonyl-containingpolyurethane-vinyl hybrid dispersions which crosslink by way ofhydrazine compounds but do not have a core-shell structure.

[0006] EP-A 0 555 774 discloses copolymer dispersions formed bycopolymerizing monomers having carbonyl groups and carboxyl groups.These dispersions also do not have a core-shell structure, as they areprepared in a single-stage polymerization with no change in thecomposition of the monomer mixture. The binders prepared with thesedispersions are crosslinked by reaction with the polyamines employed asneutralizing agents. With these products, first a high proportion ofcarbonyl groups is required to achieve sufficient crosslinking densityof the coating films and second this high proportion of correspondingmonomers results, during the copolymerization, in the formation of gelspecks and coagulum whose removal can only be accomplished at greatexpense in terms of time and apparatus. In addition, the polyamineemployed as crosslinking component leads to severe yellowing of thecoating film and so to problems in numerous applications.

[0007] AT-B 402 504 describes self-crosslinking aqueous polymerdispersions which are prepared in a two-stage process. In this process,the composition of the monomer mixture for the second stage of thepolymerization differs from that of the first stage. These copolymerdispersions have small fractions of carbonyl groups and permit highcrosslinking densities without forming the coagulum or gel specks thatare difficult to remove. However, the polyamines employed ascrosslinking component likewise occasion severe yellowing of theresulting coating films.

[0008] European Patent Application EP-A 0 795 568 describes aqueouspolymer dispersions having a core-shell structure in the core of whichat least 50% of the monomers which are employed are those whosehomopolymers have a glass temperature of below 0° C. while theproportion of such monomers employed in the shell is less than 45%.Difunctional acid hydrazides can also be added to the dispersion. Wheresuch hydrazides are added in the examples, the monomer mixture for theshell of the polymer particles also includes a monomer that containsketone groups. In this case, the monomer composition is selected inaccordance with the desired minimum film-forming temperatures.

[0009] In AT-B 403 478, the dispersions known from AT-B 402 504 arecombined with polyfunctional isocyanates of low molar mass to formtwo-component binders. Although it is possible in this way to providecoating materials which have a reduced tendency to yellow and animproved resistance to water, chemicals and light exposure, there aredisadvantages associated with these coating materials. These include thecomplex preparation of the coating material, the limited pot life,prolonged drying time, and relatively low film hardness.

OBJECT OF THE INVENTION

[0010] It has surprisingly now been found that aqueous copolymerdispersions prepared in accordance with AT-B 402 504 by a two-stageprocess in which monomers having in each case carbonyl and carboxylgroups are employed only in the first stage (which leads to the core ofthe particles) can be crosslinked, following neutralization of thecarboxyl groups by adding small amounts of ammonia, amines or aqueousalkalis, with polyfunctional hydrazides and lead to binders having asufficient pot life which can be processed to give coating materialshaving high film hardness, good resistance to mechanical and chemicalexposure, rapid drying, and little or no tendency to yellow.

SUMMARY OF THE INVENTION

[0011] The invention accordingly provides aqueous self-crosslinkingcopolymer dispersions ABC obtainable by free-radically initiatedcopolymerization in the first stage of a monomer mixture A comprisingmass fractions in the mixture of

[0012] A1 from about 2 to about 55%, preferably from about 4 to about45% and, with particular preference, from about 6 to about 40% ofolefinically unsaturated monomers having in each case at least onecarbonyl group per molecule,

[0013] A2 from about 0.5 to about 20%, preferably from about 1 to about15% and, with particular preference, from about 3 to about 12% ofα,β-olefinically unsaturated carboxylic acids or monoesters ofα,β-olefinically unsaturated dicarboxylic acids with linear, branched orcyclic alcohols having 1 to 15 carbon atoms,

[0014] A3 from about 20 to about 70%, preferably from about 22 to about60% and, with particular preference, from about 24 to about 50% ofolefinically unsaturated monomers selected from vinylaromatic compounds,n-butyl methacrylate and also alkyl esters of α,β-olefinicallyunsaturated carboxylic acids or dialkyl esters of α,β-olefinicallyunsaturated dicarboxylic acids, the alkyl groups being selected fromlinear and branched alkyl groups having up to 3 carbon atoms in thealkyl radical and cyclic and polycyclic alkyl groups having 5 to 15carbon atoms in the alkyl group,

[0015] A4 from about 10 to about 60%, preferably from about 15 to about50% and, with particular preference, from about 20 to about 45% ofesters selected from alkyl esters of α,β-olefinically unsaturatedcarboxylic acids or dialkyl esters of α,β-olefinically unsaturateddicarboxylic acids, the alkyl groups being selected from linear andbranched alkyl groups having more than 3 carbon atoms in the alkylradical, with the exception of n-butyl methacrylate, and

[0016] A5 from 0 to about 25%, preferably from about 2 to about 20% and,with particular preference, from about 5 to about 15% of otherfree-radically polymerizable monomers selected from vinyl esters ofaliphatic saturated carboxylic acids having 2 to 18 carbon atoms,hydroxyalkyl esters, nitrites and amides of α,β-unsaturated carboxylicacids,

[0017] the sum of the mass fractions of components A1 to A5 necessarilybeing 100%, and by subsequent addition of a second monomer mixture B andfurther free-radically initiated polymerization of this monomer mixturein the second stage, the mixture B comprising mass fractions of

[0018] B1 from about 30 to about 90%, preferably from about 40 to about80% and, with particular preference, from about 50 to about 75% ofolefinically unsaturated monomers selected from vinylaromatic compounds,n-butyl methacrylate and also alkyl esters of α,β-olefinicallyunsaturated carboxylic acids or dialkyl esters of α,β-olefinicallyunsaturated dicarboxylic acids, the alkyl groups being selected fromlinear and branched alkyl groups having up to 3 carbon atoms in thealkyl radical and cyclic and polycyclic alkyl groups having 5 to 15carbon atoms in the alkyl group,

[0019] B2 from about 10 to about 60%, preferably from about 20 to about50% and, with particular preference, from about 25 to about 40% ofesters selected from alkyl esters of α,β-olefinically unsaturatedcarboxylic acids or dialkyl esters of α,β-olefinically unsaturateddicarboxylic acids, the alkyl groups being selected from linear andbranched alkyl groups having more than 3 carbon atoms in the alkylradical, with the exception of n-butyl methacrylate, and

[0020] B3 from 0 to about 40%, preferably from about 5 to about 30% and,with particular preference, from about 10 to about 25% of otherfree-radically polymerizable monomers selected from vinyl esters ofaliphatic saturated carboxylic acids having 2 to 18 carbon atoms,hydroxyalkyl esters, nitrites and amides of α,β-unsaturated carboxylicacids,

[0021] the sum of the mass fractions of components B1 to B3 necessarilybeing 100%, and the ratio of the mass of the monomer mixture A to themass of the monomer mixture B is from about 50:50 to about 95:5,preferably from about 60:40 to about 90:10.

[0022] The copolymers AB obtainable in this way preferably contain,based on the mass of the solids of the dispersion, from about 0.2 toabout 1.7 mol/kg of carbonyl groups and from about 0.15 to about 1.6mol/kg of carboxyl groups. The amount of substance of the carboxylgroups here is always lower than the amount of substance of the carbonylgroups; preferably, the ratio of the amount of substance of the carboxylgroups n(—COOH) to the amount of substance of the carbonyl groups n(>CO)is from about 0.5 to about 0.95 mol/mol, with particular preference fromabout 0.75 to about 0.9 mol/mol.

[0023] The resulting dispersions of the copolymers AB are neutralizedfollowing the polymerization by adding ammonia, amines or aqueousalkalis, the amount in which the neutralizing agents are added beingsuch that it is sufficient to neutralize from 0 to about 120% of thecarboxyl groups present.

[0024] To the dispersion neutralized in this way there are subsequentlyadded compounds C having at least two hydrazine or hydrazide groups permolecule, in an amount such that the ratio r of the sum of the amount ofsubstance of hydrazine groups n(—NH—NH₂) and the amount of substance ofhydrazide groups n(—CO—NH—NH₂) to the amount of substance of thecarbonyl groups n(>CO) is from about 0.5 to about 1.1 mol/mol,preferably between about 0.8 and about 1.0 mol/mol.

[0025] The invention additionally provides a process for preparing thecopolymer dispersions of the invention, in which water with or withoutemulsifiers is introduced as initial charge and heated to the desiredreaction temperature, a mixture comprising water, emulsifiers ifdesired, the monomer mixture A, and a free-radical polymerizationinitiator is metered in to this initial charge, the polymerization iscontinued until at least 95% of the monomers have reacted, then a secondmixture comprising water, emulsifiers if desired, and also the monomermixture B and a further free radical forming polymerization initiator ismetered in and the polymerization is subsequently continued until theresidual monomer content has fallen below 1%. The resulting dispersionis cooled and admixed, with stirring, with the neutralizing agent,preferably in the form of an aqueous solution. Subsequently, thehydrazine compound or hydrazide compound C is added with stirring to theneutralized dispersion of the copolymer AB to form the self-crosslinkingdispersion ABC.

[0026] Finally, the invention also provides for the use of thesedispersions as binders for storage-stable one-component coatingmaterials which crosslink at room temperature or at elevatedtemperature.

[0027] DETAILED DESCRIPTION OF THE INVENTION

[0028] The amines or alkalis used if desired for neutralization improvethe stability of the aqueous copolymer dispersions.

[0029] Olefinically unsaturated monomers containing carbonyl groups areemployed as monomer component A1. Preference is given to the use oflinear, branched and cyclic aliphatic compounds having 4 to 20 carbonatoms and each containing at least one carbonyl group and one ethylenicdouble bond. To a minor extent (up to 10% of the mass of the monomersA1) it is also possible to employ compounds having two or morepolymerizable double bonds, which leads to crosslinking of thecopolymer. Particular preference is given to the use of α,β-olefinicallyunsaturated monomers such as N-diacetone(meth)acrylamide and(meth)acrylic acid acetoacetoxyalkyl esters whose alkylene group isselected from 1,2-ethylene, 1,2- and 1,3-propylene, 1,4-butylene and1,6-hexylene and also 1,5-(3-oxa)pentylene and 1,8-(3,6-dioxa)octylenegroups, especially the ethyl esters.

[0030] The monomers A2 are preferably α,β-unsaturated carboxylic acidshaving 3 to 4 carbon atoms, such as acrylic acid, methacrylic acid,crotonic and isocrotonic acid and also vinylacetic acid. Monoesters ofα,β-unsaturated carboxylic acids with linear, branched or cyclicalcohols having 1 to 15 carbon atoms can also be employed, thedicarboxylic acids preferably having 4 to 6 carbon atoms. Preference isgiven to monomethyl and monoethyl esters of maleic acid, fumaric acid,and also citraconic, mesaconic, itaconic and glutaconic acid.

[0031] Of the monomers A3, preference is given to the esters ofmethanol, ethanol, n- and isopropanol with acrylic and methacrylic acidand to the diesters of said alcohols with the dicarboxylic acidsspecified under A2, and also to n-butyl methacrylate and, of thevinylaromatic compounds, especially styrene, p-methylstyrene and theisomer mixture known as “vinyltoluene”. Particular preference is givento methyl and ethyl (meth)acrylate, n-butyl methacrylate, styrene, anddimethyl maleate.

[0032] As monomers A4 it is preferred to employ the esters of n-, sec-and tert-butanol, the isomeric pentanols and the higher alcohols such asn-hexanol and 2-ethylhexyl alcohol with α,β-unsaturated carboxylic acidsselected from acrylic and methacrylic acid, vinylacetic acid, maleicacid and fumaric acid; in the case of the dicarboxylic acids referredto, the diesters are used, and n-butyl methacrylate is excluded.

[0033] As examples of the hydroxyalkyl esters of olefinicallyunsaturated carboxylic acids as monomer component A5 mention may be madeof hydroxyethyl and 2-hydroxypropyl (meth)acrylate, (meth)acrylonitrile,(meth)acrylamide and, for the vinyl esters, of vinyl acetate.

[0034] In the second stage a polymer having a different chemicalstructure is produced by adding the monomer mixture B alone or togetherwith new initiators.

[0035] The monomers B1 correspond to those specified under A3, themonomers B2 to those specified under A4, and the monomers B3, finally,to those specified under A5. The monomer mixture B is therefore freefrom compounds having functional groups selected from carbonyl andcarboxyl groups.

[0036] The compounds C with hydrazine or hydrazide functionalitycomprise two or more hydrazine or hydrazide groups and preferably havean average molar mass (M_(n)) of less than about 1000 g/mol. Examples ofsuch compounds are bishydrazides of dicarboxylic acids having 2 to 12carbon atoms such as the bishydrazides of oxalic acid, malonic acid,succinic acid, glutaric acid, adipic acid, pinalic acid, suberic acid,azelic acid, sebacic acid or the isomeric phthalic acids; carbonicbishydrazide, alkylene- or cycloalkylene-bissemicarbazides,N,N′-diaminoguanidine, alkylene-bishydrazines such asN,N′-diaminopiperazine, arylenebishydrazines such as phenylene- ornaphthylenebishydrazine, and alkylenebissemicarbazides. Compounds C ofhigher functionality are, for example, the hydrazides ofnitrilotriacetic acid or of ethylenediaminetetracetic acid.

[0037] The copolymer dispersions of the invention have excellentstability on storage and produce films having good resistanceproperties. They can be employed as binders for industrial coatings andprimers. In addition, they can be used to formulate transparent coatingmaterials which can be used in turn to coat wood, plastic, leather orpaper.

[0038] The crosslinking of the copolymer dispersions takes place byreaction of the hydrazine or hydrazide groups of the compounds C withthe carbonyl groups of the copolymer dispersions AB at temperatures aslow as room temperature following the evaporation of a substantialproportion of water.

[0039] The formulation of water-dilutable coating materials using thebinders prepared in accordance with the invention, and the applicationof such coating materials, are known to the skilled worker.

[0040] The examples which follow illustrate the invention withoutrestricting it in its scope. In the examples below, as in the text whichprecedes them, all figures with the unit “%” are mass fractions unlessspecified otherwise. “Parts” are always parts by mass. Concentrationfigures in are mass fractions of the dissolved substance in the solution(in g/100 g)).

EXAMPLES Example 1

[0041] In a reactor suitable for emulsion copolymerization with refluxcondenser, thermometer and two feed vessels a mixture of 360 parts ofdemineralized water, 24 parts of ®Triton X 200 (sodium alkylarylpolyether sulfonate, manufacturer: Rohm & Haas, USA) and 5.4 parts of(®Triton X 165 (octylphenol ethoxylate, manufacturer: Rohm & Haas, USA)was homogenized with stirring.

[0042] The feed vessel A was charged with a homogeneous emulsionconsisting of 1150 parts of demineralized water, 24 parts of Triton X200, 10 parts of Triton X 165, 3.2 parts of ammonium peroxodisulfate,165 parts of n-butyl methacrylate, 280 parts of n-butyl acrylate, 275parts of styrene, 140 parts of acetoacetoxyethyl methacrylate and 40parts of methacrylic acid. 5% of this initial emulsion was run into thereactor. The contents of the reactor were heated to 85° C. with stirringand held at this temperature for 10 minutes. Then the remaining contentsof the feed vessel A were metered into the reactor at a uniform rateover 120 minutes at 85° C.

[0043] Subsequently, a homogeneous emulsion of 100 parts ofdemineralized water, 3.1 parts of Triton X 200, 2.4 parts of Triton X165, 30 parts of n-butyl acrylate, 70 parts of styrene and 0.8 part ofammonium peroxodisulfate were metered in over 30 minutes at 85° C. fromthe feed vessel B. Following the end of the addition, the contents ofthe reactor were heated to 88° C. and held at this temperature for 120minutes. Finally, the reaction mixture was cooled to 25° C. and adjustedto a pH of 5.5 by adding 10% aqueous ammonia solution. Thereafter, 51.2parts of adipic dihydrazide were added over the course of 30 minutes.This gave an opalescent dispersion having a mass fraction of solids of38.8% and an average particle size of 105 nm. The pH was 5.5.

Examples 2 to 7

[0044] The procedure of Example 1 was repeated. The compositions of theinitial charges to the reactor and of the feeds, plus alteredpolymerization parameters, can be taken from Table 1, in which thefollowing abbreviations are used: ADH Adipic dihydrazide ODH Oxalicdihydrazide AAEMA Acetoacetoxyethylmethacrylate APS Ammoniumperoxodisulphate AA Acrylic acid BA Butyl acrylate BMA Butylmethacrylate BV ®Hostapal BV conc. (Clariant GmbH, DE) DAADiacetoneacrylamide DBF Dibutyl fumarate DMEA Dimethylethanolamine DWDemineralized water EHA 2-Ethylhexyl acrylate HBA 4-Hydroxybutylacrylate HEMA 2-Hydroxyethylmethacrylate MA Methacrylic acid pMSTp-Methylstyrene NH₃ Ammonia ST Styrene X 165 ®Triton X 200 (Rohm & Haas,USA) X 200 ®Triton X 200 (Rohm & Haas, USA) X 305 ®Triton X 305 (Rohm &Haas, USA) (alkylaryl polyether alcohol)

[0045] TABLE 1 Example 1 2 3 4 Initial charge 360 DW 420 DW 325 DW 325DW 24 X 200 25 X 200 25 X 200 10 BV 5.4 X 165 7 X 165 7 X 165 7 X 165Feed A 1150 DW 1210 DW 1100 DW 1000 DW 24 X 200 25 X 200 25 X 200 10 BV10 X 165 5.6 X 165 5.6 X 165 5.6 X 165 3.2 APS 5 APS 5 APS 5 APS 165 BMA195 MMA 185 EHA 250 ST 280 BA 200 BA 420 BMA 285 BA 275 ST 320 AAEMA 100BA 120 DAA 140 AAEMA 85 AA 70 DAA 45 MA 40 MA 25 AA Fraction of feed Ain the 5 7.5 7.5 10 initial charge (%) Feed time A (min) 120 100 100 90Feed B 100 DW 200 DW 200 DW 250 DW 3.1 X 200 6 X 200 6 X 200 5 BV 2.4 X165 1.4 X 165 1.4 X 165 2 X 165 0.8 APS 0.8 APS 0.8 APS 1 APS 30 BA 150BMA 150 ST 100 pMST 70 ST 50 BA 50 EHA 150 BA 50 BMA Feed time B (min)30 45 45 60 Neutralizing agent 55 NH₃ 87 DMEA 24 NH₃ 47 NH₃ (10%) (10%)(10%) (10%) Crosslinker 51.2 ADH 110.6 ADH 24.4 ODH 58.7 ADH pH (as 10%strength 5.5 6.2 6.4 5.8 solution in water) Example 5 6 7 Initial charge280 DW 325 DW 325 DW 10 BV 25 X 200 10 BV 7 X 305 7 X 165 7 X 165 Feed A1100 DW 1100 DW 1000 DW 8 BV 25 X 200 10 BV 5 X 305 5.6 X 165 5.6 X 1655 APS 5 APS 5 APS 150 MMA 135 EHA 200 ST 205 DBF 380 BMA 335 BA 180 DAA50 BA 120 AAEMA 65 MS 100 DAA 50 HEMA 100 HBA 45 MS 35 AA Fraction offeed A in the initial 10 7.5 10 charge (%) Feed time A (min) 90 100 90Feed B 300 DW 200 DW 250 DW 7 BV 6 X 200 5 BV 3 X 305 1.4 X 165 2 X 1651.2 APS 0.8 APS 1 APS 200 ST 150 ST 100 pMST 100 BA 50 EHA 100 BA 100BMA 50 BMA Feed time B (min) 60 45 60 Neutralizing agent 69 DMEA 27 NH₃38 NH₃ (10%) (10%) (10%) Crosslinker 92.7 ADH 31.4 ODH 41.5 ADH pH (as10% strength solution 6.0 6.5 5.8 in water)

[0046] TABLE 2 Example 1 2 3 4 5 6 7 V1 Solids content in % 38.7 37.538.3 40.0 39.1 38.5 38.5 38.8 PH 5.5 6.2 6.4 5.8 6.0 6.5 5.8 7.9 Averageparticle size in nm 105 100 115 100 95 105 100 90 n(>CO)/m⁽¹⁾ in mol/kg0.65 1.5 0.41 0.71 1.07 0.59 0.56 0.65 n(—COOH)/m⁽²⁾ in mol/kg 0.47 1.180.35 0.52 0.76 0.49 0.52 0.47 n(—COOH)/n(>CO)⁽³⁾ in mol/mol 0.72 0.790.85 0.73 0.71 0.83 0.93 0.72 r⁽⁴⁾ in mol/mol 0.90 0.85 1.00 0.95 1.000.90 0.85 0.95

[0047] Performance testing in transparent coating materials Thetransparent coating materials 1 to 5 and VI were prepared by mixing anamount of the hydrazide-containing copolymer dispersion such that themass of solids present therein was 100 g, 0.8 g of a commerciallycustomary defoamer, 0.2 g of a commercially customary leveling agent,and deionized water sufficient to give an efflux time of 25 seconds at23° C. in accordance with DIN 53 211. The results of the performancetests are summarized in Table 3: TABLE 3 Transparent coating material 12 3 4 5 V1 V2 Tack-free time in minutes 15 15 15 15 15 15 50 Sandability0 0 0 0 0 0 MIN Pendulum hardness in s 72 75 82 73 68 80 50 Acetoneresistance in s >60 >60 >60 >60 >60 >60 >60 Ethanol resistance in h 5 44 5 4 5 >8 Water resistance in h >48 >36 >48 >36 >36 >24 >48 Yellowing 11-2 1 1 1-2 4 1-2 Pot life (storage stability) >3 mths >3 mths >3mths >3 mths >3 mths >3 mths 20 hrs

[0048] Tack-free time: Drying recorder, glass strips, application of acoating film with a wet-film thickness of 150 μm, at 20° C. (statementof time in minutes until a tack-free surface is obtained)

[0049] Sandability: Veneered wood, application of a coating film with awet-film thickness of 150 μm; the parameter tested was the clogging ofabrasive paper (320 grade) after 10 strokes following a drying time of60 minutes at room temperature.

[0050] The clogging of the abrasive paper is a practical test for theuser (parquet layer, furniture maker). It refers to the attachment offreshly applied coating films to the abrasive paper in the case ofsanding prior to the application of a further coating film.

[0051] The optimum value is 0 (no clogging) although the value MIN(attachments to less than 10% of the area of the abrasive paper) is alsoaccepted.

[0052] KÖNIG pendulum hardness (DIN 53157): Glass plates, application ofa coating film with a wet-film thickness of 120 μm, drying time of 24hours at 20° C.

[0053] Resistance to acetone, ethanol and water: Glass plates,application of a coating film with a wet-film thickness of 120 μm,drying time of 24 hours at 20° C.; a cotton pad soaked with the solventwas placed on the coating film and covered with a glass beaker. The timetaken for the film to soften was measured.

[0054] Pot life: The two-component coating material is stirred at hourlyintervals. This operation is repeated until the onset of gelling.

[0055] Yellowing: 200 μm wet-film thickness on maple (veneered). Theassessment is made during storage at room temperature for 4 weeks (1=nodiscernible discoloration 5=very severe discoloration).

[0056] The above description of the invention is intended to beillustrative and not limiting. Various changes or modifications in theembodiments described may occur to those skilled in the art. These canbe made without departing from the scope and spirit of the invention.

What is claimed:
 1. An aqueous self-crosslinking copolymer dispersion,ABC, obtainable by first, conducting a free-radically initiatedcopolymerization of the monomer mixture A, which comprises massfractions in the mixture of A1 from about 2 to about 55%, ofolefinically unsaturated monomers having in each case at least onecarbonyl group per molecule, A2 from about 0.5 to about 20%, ofα,β-olefinically unsaturated carboxylic acids or monoesters ofα,β-olefinically unsaturated dicarboxylic acids with linear, branched orcyclic alcohols having 1 to 15 carbon atoms, A3 from about 20 to about70%, of olefinically unsaturated monomers selected from vinylaromaticcompounds, n-butyl methacrylate, alkyl esters of α,β-olefinicallyunsaturated carboxylic acids or dialkyl esters of α,β-olefinicallyunsaturated dicarboxylic acids, the alkyl groups being selected fromlinear and branched alkyl groups having up to 3 carbon atoms in thealkyl radical and cyclic and polycyclic alkyl groups having 5 to 15carbon atoms in the alkyl group, A4 from about 10 to about 60% byweight, of esters selected from alkyl esters of α,β-olefinicallyunsaturated carboxylic acids or dialkyl esters of α,β-olefinicallyunsaturated dicarboxylic acids, the alkyl groups being selected fromlinear and branched alkyl groups having more than 3 carbon atoms in thealkyl radical, with the exception of n-butyl methacrylate, and A5 from 0to about 25%, of other free-radically polymerizable monomers selectedfrom vinyl esters of aliphatic saturated carboxylic acids having 2 to 18carbon atoms, hydroxyalkyl esters, nitrites and amides ofα,β-unsaturated carboxylic acids,  where the sum of the mass fraction ofcompounds A1 to B5 is 100%, and subsequently adding a second monomermixture B, which comprises mass fractions in the mixture of B1 fromabout 30 to 90%, of olefinically unsaturated monomers selected fromvinylaromatic compounds, n-butyl methacrylate, alkyl esters ofα,β-olefinically unsaturated carboxylic acids or dialkyl esters ofα,β-olefinically unsaturated dicarboxylic acids, the alkyl groups beingselected from linear and branched alkyl groups having up to 3 carbonatoms in the alkyl radical and cyclic and polycyclic alkyl groups having5 to 15 carbon atoms in the alkyl group, B2 from about 10 to about 60%,of esters selected from alkyl esters of α,β-olefinically unsaturatedcarboxylic acids or dialkyl esters of α,β-olefinically unsaturateddicarboxylic acids, the alkyl groups being selected from linear andbranched alkyl groups having more than 3 carbon atoms in the alkylradical, with the exception of n-butyl methacrylate, and B3 from 0 toabout 40%, of other free-radically polymerizable monomers selected fromvinyl esters of aliphatic saturated carboxylic acids having 2 to 18carbon atoms, hydroxyalkyl esters, nitrites and amides ofα,β-unsaturated carboxylic acids,  where the sum of the mass fractionsof compounds B1 to B3 is 100% and the ratio of the mass of monomermixture A to monomer mixture B is from about 50:50 to about 95:5, andwherein initiating a second free-radically initiated polymerization ofthe monomer mixture and optionally neutralizing the dispersion afterpolymerization by adding ammonia, amines or aqueous alkali the amount ofsubstance of the carboxyl groups in copolymer AB is lower than that ofthe carbonyl groups, and adding compounds C, having at least twohydrazine or hydrazide groups per molecule in an amount such that theratio r of the sum of the amount of substance of hydrazine groupsn(—NH—NH₂) and the amount of substance of hydrazide groups n(—CO—NH—NH₂)to the amount of substance of the carbonyl groups n(>CO) is from about0.5 to about 1.1 mol/mol.
 2. An aqueous self-crosslinking copolymerdispersion ABC as claimed in claim 1, wherein the carbonyl group contentis from about 0.2 to about 1.7 mol/g and the carboxyl group content isfrom about 0.15 to about 1.6 mol/kg, based in each case on the mass ofthe solids of the dispersion.
 3. An aqueous self-crosslinking copolymerdispersion ABC as claimed in claim 1, wherein up to 10% of the mass ofthe monomers of A1 have 2 or more polymerizable double bonds.
 4. Anaqueous self-crosslinking copolymer dispersion ABC as claimed in claim1, wherein the monomers of A1 are selected fromdiacetone(meth)acrylamide and (meth)acrylic acid acetoacetoxyalkylesters whose alkylene group is selected from 1,2-ethylene, 1,2- and1,3-propylene, 1,4-butylene and 1,6-hexylene and also1,5-(3-oxa)pentylene and 1,8-(3,6-dioxa)octylene groups.
 5. An aqueousself-crosslinking copolymer dispersion ABC as claimed in claim 1,wherein the monomers of A2 are selected from acrylic acid andmethacrylic acid.
 6. An aqueous self-crosslinking copolymer dispersionABC as claimed in claim 1, wherein the monomers of A3 and of B1independently of one another are selected from methyl and ethyl(meth)acrylate and dimethyl maleate.
 7. An aqueous self-crosslinkingcopolymer dispersion ABC as claimed in claim 1, wherein the monomers ofA4 and of B2 independently of one another are selected from the acrylicand methacrylic esters of n-, sec- and isobutanol, n-hexanol and2-ethylhexanol.
 8. An aqueous self-crosslinking copolymer dispersion ABCas claimed in claim 1, wherein the monomers of A5 and of B3independently of one another are selected from styrene, vinyltoluene,p-methylstyrene and vinyl acetate.
 9. An aqueous self-crosslinkingcopolymer dispersion ABC as claimed in claim 1, wherein the compounds Care selected from oxalic and adipic dihydrazide and diaminopiperazine.10. An aqueous self-crosslinking copolymer dispersion ABA as claimed inclaim 1, wherein monomer mixture A comprises mass fraction of A1 from 2to 55%, A2 from 0.5 to 20%, A3 from 20 to 70%, A4 from 10 to 60%, A5from 0 to 25%,

and the monomer mixture B comprises mass fractions of B1 from 30 to 90%,B2 from 10 to 60%, B3 from 0 to 40%,

and the mass of the monomer mixture A to the mass of the monomer mixtureB is from 50:50 to 95:5, and the ratio r have the sum of the amount ofsubstance of hydrazine groups n(—NH—NH₂) and the amount of substance ofhydrazide groups n(—CO—NH—NH₂) to the amount of substance of thecarbonyl groups n(>CO) is from about 0.5 to about 1.1 mol/mol.
 11. Anaqueous self-crosslinking copolymer dispersion ABA as claimed in claim1, wherein monomer mixture A comprises mass fraction of A1 from about 4to about 50%, A2 from about 1 to about 15%, A3 from about 22 to about60%, A4 from about 15 to about 50%,

and the monomer mixture B comprises mass fraction of B1 from about 40 toabout 80%, B2 from about 20 to about 50%, and B3 from about 5 to about30%.


12. An aqueous self-crosslinking copolymer dispersion ABA as claimed inclaim 1, wherein monomer mixture A comprises mass fraction of A1 fromabout 6 to about 44%, A2 from about 3 to about 12%, A3 from about 24 toabout 50%, A4 from about 20 to about 45%,

and the monomer mixture B comprises mass fraction of B1 from about 50 toabout 75% B2 from about 25 to about 40% B3 from about 10 to about 25%


13. A process for preparing an aqueous self-crosslinking copolymerdispersion ABC as claimed in claim 1, which comprises in the first stageconducting a free-radically initiated copolymerization of the monomermixture A, subsequently initiating a second polymerization step byadding a first monomer mixture B with or without further polymerizationinitiator, and adding to the resultant aqueous dispersion, directly orfollowing at least partial neutralization, a compound C having at leasttwo functional groups selected from hydrazine and hydrazide groups. 14.A binder for one-component coating materials, comprising a copolymerdispersion as claimed in claim
 1. 15. A coating material which comprisesa copolymer dispersion as claimed in claim
 1. 16. The coating materialas claimed in claim 15, which is transparent.
 17. A coated substratewhich is coated by a coating material as claimed in claim
 15. 18. Thecoated substrate according to claim 17, wherein the substrate is wood,plastic, leather or paper.